Method for ascertaining at least one malfunction of a conductive conductivity sensor

Abstract

A method and a sensor for ascertaining at least one malfunction of a conductive conductivity sensor having at least two electrodes applying a first electrical variable to the electrodes measuring at least a second electrical variable on the electrodes and deciding whether a malfunction is present based on measuring the second electrical variable. The second electrical variable is located in a first range when measuring the medium when no malfunction is present, and the second electrical variable is located in a second range in the case of a first malfunction, especially when the conductivity sensor is located at least partially outside of the medium, and the second electrical variable is located in a third range when a second malfunction is present, especially an electrode break or a break in a line to the electrodes.

The invention claimed is: 
     
       1. A method for ascertaining at least one malfunction of a conductive conductivity sensor having at least two electrodes, wherein the conductivity sensor is applied for measuring conductivity of a medium, comprising the steps of:
 applying a first electrical variable to the electrodes; 
 measuring at least a second electrical variable on the electrodes; and 
 deciding whether a malfunction is present based on measuring the second electrical variable, wherein: 
 the second electrical variable is located in a first range when measuring the medium when no malfunction is present; 
 the second electrical variable is located in a second range in the case of a first malfunction, when the conductivity sensor is located at least partially outside of the medium; and 
 the second electrical variable is located in a third range when a second malfunction is present, a second malfunction in the form of an electrode break or a break in a line to the electrodes; 
 wherein the capacitance between the electrodes is used as the second electrical variable. 
 
     
     
       2. The method as claimed in  claim 1 , wherein:
 an electrical alternating variable is used as the first electrical variable. 
 
     
     
       3. A conductivity sensor for performing a method, when the conductivity sensor is applied for measuring conductivity of a medium, of ascertaining at least one malfunction of the conductivity sensor, the conductivity sensor comprising:
 at least two electrodes; 
 an electrical circuit; 
 wherein the electrical circuit is configured to apply a first electrical variable to the electrodes, to measure at least a second electrical variable on the electrodes, and to decide whether a malfunction is present based on measuring the second electrical variable; 
 wherein the second electrical variable is located in a first range when measuring the medium when no malfunction is present, the second electrical variable is located in second range in the case of a first malfunction when the conductivity sensor is located at least partially outside of the medium, and the second electrical variable is located in a third range when a second malfunction in the form of an electrode break or a break in a line to the electrodes is present; and 
 wherein the capacitance between the electrodes is used as the second electrical variable. 
 
     
     
       4. The conductivity sensor for performing a method as claimed in  claim 3 , wherein:
 the conductivity sensor includes at least four electrodes, which are combined pairwise to form a first electrode pair and a second electrode pair; and 
 a circuit for switching the first electrical variable between first electrode pair and second electrode pair is provided.